Medical devices may be coated so that the surfaces of such devices have desired properties or effects. For example, it may be useful to coat medical devices to provide for the localized delivery of therapeutic agents to target locations within the body, such as to treat localized disease (e.g., heart disease) or occluded body lumens. Localized drug delivery may avoid some of the problems of systemic drug administration, which may be accompanied by unwanted effects on parts of the body which are not to be treated. Additionally, treatment of the afflicted part of the body may require a high concentration of therapeutic agent that may not be achievable by systemic administration. Localized drug delivery may be achieved, for example, by coating balloon catheters, stents and the like with the therapeutic agent to be locally delivered. The coating on medical devices may provide for controlled release, which may include long-term or sustained release, of a bioactive material.
Aside from facilitating localized drug delivery, medical devices may be coated with materials to provide beneficial surface properties. For example, medical devices are often coated with radiopaque materials to allow for fluoroscopic visualization during placement in the body. It is also useful to coat certain devices to achieve enhanced biocompatibility and to improve surface properties such as lubriciousness.
The type, thickness and other properties of the polymer and/or therapeutic agent may be chosen to create different release kinetics. Coatings may be applied to medical devices by processes such as dipping, spraying, vapor deposition, plasma polymerization, and electrodeposition. Although these processes may be used to produce satisfactory coatings, they are all subject to a drawback. After the coating process, stents may need to endure further handling as part of the manufacturing process. For instance, stents may need to be crimped onto a balloon. This further handling may cause deformities in the coating. Additionally, the drying process, or even the coating process itself, may lead to uneven coating and/or an uneven coating surface. An uneven coating surface may lead to a less predictable Kinetic Drug Release (KDR), which may lead to an individual stent or a batch of stents (or other medical devices) failing quality control. A non-uniform or uneven coating may lead to the unit failing KDR, drug uniformity and coating thickness specifications.
Therefore, an uneven coating surface has traditionally been an unwanted, though often inevitable, result of the manufacturing process. There is, therefore, a need for a cost-effective method of coating devices that results in uniform, defect-free coatings and uniform drug doses per unit device. The method would allow for better control of the sensitivity of the bioactive material and would also reduce variations in the coating properties between medical devices.
To alter the KDR profile of a Drug Eluting (DE) product, typically either the formulation of the drug/carrier or application of an overcoat is required. Each of these methods involves altering the chemistry and potentially impacting the efficacy/bio-compatibility of the product.